1. Field of the Invention
The present invention relates generally to an apparatus for variably controlling the lift opening movements and valve opening duration periods of the intake and exhaust valves of an internal combustion engine.
The terminology "internal combustion engine" as employed herein is intended to connote all types of internal combustion engines having combustion chambers and wherein the flow of the combustible charge into the combustion chamber and the flow of burned material or exhaust gases from the combustion chamber are controlled by intake and exhaust valves. Thus, included within the terminology "internal combustion engine" is the multitude of conventional engine designs which include various types of cylinder arrangements, various cam arrangements, and either two-stroke or four-stroke cycle design.
In particular, the present invention relates to a camming apparatus wherein an intake cam member and an exhaust cam member are axially slidable responsive to the speed of the engine to provide variable control of the lift and duration of the intake and exhaust valves of the engine, with a hydraulic cam-action transmitting member being employed in transmitting camming action from the cam members to the valves.
2. Description of the Prior Art
In internal combustion engines having combustion chambers each provided with an intake and exhaust valve, various types of conventional valve operation means have heretofore been employed. Such valves are generally opened by cam action, and such cam action may be transmitted either directly against the end of the valve stems of the valves, or alternatively by a system of cooperating cam followers, push-rods and rocker arms, or other linkage members. The valves are generally closed by coil springs or the like which resist cam action. Such prior art techniques, however, inherently are afflicted with a common major disadvantage in that valve timing (the duration of lift for both intake and exhaust valves) is inflexible. In other words, the duration of lift for the valves remains the same, regardless of the rpm of the engine itself.
Such inflexibility in conventional valve operation means leads to the undesirable situation of providing optimum valve timing for the engine only within a very limited range of engine speeds, with combustion efficiency seriously decreasing at engine speeds outside of such limited optimum range. Although theoretically it is sufficient to maintain the intake valve open during the intake stroke and the exhaust valve open during the exhaust stroke, in conventional engines the valve timing is such that compromising overlap periods are provided. In other words, the intake valve is adapted to open prior to completion of the exhaust stroke in order to sufficiently fill the combustion chamber with a combustible charge and is adapted to close after the compression stroke has commenced in order to confine an increased volume of combustible mixture within the cylinder. With regard to the exhaust valve, it is adapted to open prior to the end of the expansion stroke and remains open into the intake stroke so as to purge the combustion chamber of the greatest possible amount of burned material or exhaust gases.
With such fixed overlap periods as mentioned above, engine start-up, idle and low-speed performance is seriously detrimentally affected, with incomplete combustion and high emissions levels, mainly because at low-range torque conditions best performance can only be achieved by elimination of the aforementioned fixed valve overlap. Conversely, at faster engine speeds, an increased overlap period is desirable due to increased friction and inertial forces, and increased duration and lift for the intake and exhaust valves provides increased combustible charge induction as well as providing increased purging of the exhaust gas from the chamber. Consequently, the fixed overlap periods found in conventional valve operating means represent a mere compromise between optimum low-speed and high-speed engine conditions, and the resultant inefficiency thereby produced leads to increased air pollution as well as poor engine performance.
Illustrative of prior art techniques in the field of internal combustion engine valve operation are: the "CAM SHAFT" disclosed in U.S. Pat. No. 1,651,402 issued in 1926 to Midgley; the "MEANS FOR STARTING AN INTERNAL COMBUSTION ENGINE" disclosed in U.S. Pat. No. 2,069,587 issued in 1937 to Mattern; the "METHOD AND APPARATUS FOR CONTROL OF VALVE OPERATION" disclosed in U.S. Pat. No. 3,730,150 issued in 1973 to Codner, Jr.; the "INTERNAL COMBUSTION ENGINE" disclosed in U.S. Pat. No. 3,915,129 issued in 1975 to Rust et al; and the "CAMSHAFT FOR CONTROLLING VARIABLY OPENING VALVES" issued in 1976 to Dyer.
The above-mentioned U.S. Pat. No. 3,730,150 to Codner, Jr. discloses an apparatus for controlling valve operation in an internal combustion engine by means of an axially shiftable camshaft having lobes formed with a ramp contour which varies in axial extent such that selected contours of the lobe are brought into cooperation with cam followers to provide duration and overlap periods matching desired engine performance. The valve duration periods are varied in accordance with a change in engine speed to thus increase or decrease lift duration and overlap periods, responsive to an increase or decrease in engine speed. Cam action is transmitted to the intake and exhaust valves by a conventional type of arrangement including a roller tappet with a cam-following roller. A push rod is connected to the tappet and extends to a rocker arm having an arm projecting against the valve stem. Alternatively, and also in a substantially conventional manner, in an overhead cam arrangement there is provided a hydraulic lash adjuster with a cam follower arm pivotally connected thereto. The cam follower arm serves as a lever acting against the valve stem to effect valve operation. Although the variable valve lift duration and overlap periods provided by the Codner, Jr. arrangement presents an improvement over conventional fixed valve lift duration periods, the cam action is transmitted in a substantially conventional manner from the lobes of the axially shiftable cam shaft to the valves themselves.
With conventional mechanical cam follower arrangements, such as those employed in the above-mentioned Codner, Jr. arrangement, there is normally incorporated either hydraulic lifters or hydraulic lash adjusters provided for eliminating clearance in the valve train and at the same time compensating for linear expansion and contraction due to temperature changes. The remainder of the cam action transmission means in conventional arrangements are generally mechanical, with cooperating push rods, rocker arms, etc. Generally, such conventional arrangements represent mechanically complex mechanisms which are ofttimes deficient in effectively duplicating the exact shape and lift of the cams during cam action transmission to the valve stems. Also, such conventional arrangements include a large number of moving parts, are subject to frictional forces between relatively moving parts, and generally do not present completely satisfactory and efficient means for transmission of the cam action to the valve stems.
The present invention provides an apparatus which affords a very wide range of valve lift opening movements, together with a wide range of valve opening duration periods, and generally provides more efficient valve lift control than the aforementioned prior art techniques. The apparatus according to the present invention eliminates the disadvantages and shortcomings attendant with conventional and prior art valve operating techniques, and at the same time provides an apparatus and method which employs a minimum of parts, provides maximum efficiency, and may be manufactured at a reduced costs.